1. Technical Field
Exemplary embodiments of the present disclosure generally relate to an image forming apparatus.
2. Description of the Related Art
Image forming apparatuses are known that employ an electrophotographic process as described below to form a toner image. That is, a surface of a photoreceptor serving as an electrostatic latent image bearer is uniformly charged by a charging device to an appropriate value by output of a charging bias having a value approximately the same as a target value from a power source. Then, by optically scanning the uniformly charged surface of the photoreceptor with a writing light beam, an electrostatic latent image is formed on the surface of the photoreceptor. Next, the electrostatic latent image on the surface of the photoreceptor is moved to a developing position opposite a developing device and the electrostatic latent image is developed with the developing device to obtain a toner image.
It is to be noted that, in developing by outputting a developing bias having a value approximately the same as a target value from a developing power source and supplying the developing bias to a developing roller of the developing device, an appropriate potential difference is generated between the developing roller and a background portion of the photoreceptor. Accordingly, toner adherence to the background portion of the photoreceptor called background fogging is suppressed. After obtaining the toner image on the surface of the photoreceptor by developing, the toner image is transferred from the surface of the photoreceptor to a recording sheet between a transfer roller and the photoreceptor.
Other types of image forming apparatuses also employ an electrophotographic process to form a toner image, but include a mechanism to suppress a transfer bias output error from a transfer power source. More specifically, in the transfer power source that outputs the transfer bias applied to a transfer roller, error is generated with respect to each transfer bias output value due to individual differences of voltage dividing resistances. In order to respond to such, a controller reads an adjustment value investigated and obtained in advance from prior tests from a nonvolatile memory. By adjusting a control signal that is output to the transfer power source based on the adjustment value, actual output value of the transfer bias approaches a target value, and transfer bias output error is suppressed.
Output error is not specific to the transfer power source and may be generated in the power source or the developing power source. Generally, in the field of image forming apparatuses, power sources having an output within +−3% with respect to a target output are widely employed to keep manufacturing costs low. In other words, an output value of the charging bias or the developing bias may be off by approximately +−3% from a target value, respectively.
When the charging bias is off from the target value, an aimed value of a potential of a background portion of the photoreceptor is off. When the developing bias is off from the target value, an aimed value of a potential of a surface of the developing roller is off. Accordingly, when the aimed value of the potential of the background portion of the photoreceptor or the aimed value of the potential of the surface of the developing roller is off, excess or deficiency may be generated in a background potential that is a potential difference between the surface of the developing roller and the background portion of the photoreceptor.
As a result, however, various problems may occur. For example, when the background potential is insufficient, toner on a surface of the developing roller transfers to a surface of the background portion of the photoreceptor, generating background fogging. In a case in which a two-component development method employing a two-component developer including toner and magnetic carrier is used, when the background potential is excessive, a phenomenon called carrier adhesion occurs, in which magnetic carrier of the two-component developer on the surface of the developing roller transfers to the surface of the photoreceptor.